Fundamentals - App start up

• Razor Pages

• MVC controllers with views

• Web API with controllers

• Minimal APIs

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddRazorPages();
builder.Services.AddControllersWithViews();

var app = builder.Build();

// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Error");
    app.UseHsts();
}

app.UseHttpsRedirection();
app.UseStaticFiles();

app.UseAuthorization();

app.MapGet("/hi", () => "Hello!");

app.MapDefaultControllerRoute();
app.MapRazorPages();

app.Run();

Extend Startup with startup filters

• To configure middleware at the beginning or end of an app's middleware pipeline without an explicit call to Use{Middleware}. Use IStartupFilter to add defaults to the beginning of the pipeline without explicitly registering the default middleware. IStartupFilter allows a different component to call Use{Middleware} on behalf of the app author.

• To create a pipeline of Configure methods. IStartupFilter.Configure can set a middleware to run before or after middleware added by libraries.

public class RequestSetOptionsMiddleware
{
    private readonly RequestDelegate _next;

    public RequestSetOptionsMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    // Test with https://localhost:5001/Privacy/?option=Hello
    public async Task Invoke(HttpContext httpContext)
    {
        var option = httpContext.Request.Query["option"];

        if (!string.IsNullOrWhiteSpace(option))
        {
            httpContext.Items["option"] = WebUtility.HtmlEncode(option);
        }

        await _next(httpContext);
    }
}

namespace WebStartup.Middleware;
// <snippet1>
public class RequestSetOptionsStartupFilter : IStartupFilter
{
    public Action<IApplicationBuilder> Configure(Action<IApplicationBuilder> next)
    {
        return builder =>
        {
            builder.UseMiddleware<RequestSetOptionsMiddleware>();
            next(builder);
        };
    }
}
// </snippet1>

using WebStartup.Middleware;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddRazorPages();
builder.Services.AddTransient<IStartupFilter,
                      RequestSetOptionsStartupFilter>();

var app = builder.Build();

if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Error");
    app.UseHsts();
}

app.UseHttpsRedirection();
app.UseStaticFiles();

app.UseRouting();

app.UseAuthorization();

app.MapRazorPages();

app.Run();

@page
@model PrivacyModel
@{
    ViewData["Title"] = "Privacy Policy";
}
<h1>@ViewData["Title"]</h1>

<p> Append query string ?option=hello</p>
Option String: @HttpContext.Items["option"];

• Multiple IStartupFilter implementations may interact with the same objects. If ordering is important, order their IStartupFilter service registrations to match the order that their middlewares should run.

• Libraries may add middleware with one or more IStartupFilter implementations that run before or after other app middleware registered with IStartupFilter. To invoke an IStartupFilter middleware before a middleware added by a library's IStartupFilter:

  • Position the service registration before the library is added to the service container.

  • To invoke afterward, position the service registration after the library is added.

Add configuration at startup from an external assembly

Startup, ConfigureServices, and Configure

• Use Startup with the minimal hosting model

• The ASP.NET Core 5.0 version of this article:

  • The ConfigureServices method

  • The Configure method

Ref: App startup in ASP.NET Core